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Did the earth always look like it did today?

How has life changed since the formation of earth?

What forces have changed the biodiversity on earth?

Chapter 4: Evolution and Biodiversity

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Why is there life on Earth?

• The conditions on Earth are "just right" for life to exist.• What conditions are important?

• Distance from sun + spin = Temperature is just right (liquid water)

• Size = gravity to keep atmosphere, molten core

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How did life come to exist on earth?

• Chemical evolution (1 billion years)> Organic molecules and biopolymers> *Cell membrane + genetic material!> Evidence: radioactive elements in primitive rocks

and fossils.> Miller and Urey famously attempted to replicate the

conditions of primitive earth to show by example that life could form from the molecules and energy available in the atmosphere and water.

http://www.chem.duke.edu/~jds/cruise_chem/Exobiology/miller.html

Primitive atmosphere: Methane, ammonia, hydrogen, water

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How did life come to exist on earth?

• Biological evolution (3.7 billion years)> Single celled prokaryotes to multicellular organisms> What process creates this diversity?

– Evolution by natural selection> Evidence for biological evolution

– Fossil record– Ice cores– Chemical/DNA analysis

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Evolution by Natural Selection

• Wallace and Darwin• In order for natural selection to occur, there must be:

> Variation amongst individuals in a population> Variation must be heritable

– source of variation is mutation and must be in a cell that is inherited by offspring

« caused by mutagens or mistakes during DNA replication

> Traits must lead to differential reproduction– More advantageous trait = more offspring. Over

time, the population changes so that this trait is more prevalent

– adaptation or adaptive trait is any heritable trait that allows an organism to survive and reproduce.

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What other options are there?

• When environmental conditions change, a population has 3 options> adapt> migrate> become extinct

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Evolution by Natural Selection

• Important to remember:> Natural selection happens at the individual level> Evolution happens at the population level

http://evolution.berkeley.edu/evolibrary/article/evo_25

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Limitations to natural selection

1. Gene pool limits a population's ability to adapt--you can only select from traits you have. You can't create new ones (except by chance through mutation).

2. Reproductive capacity can limit a population's ability to adapt

> Organisms that reproduce rapidly (weeds, bacteria, cockroaches, mice) adapt quickly

> Organisms that reproduce slowly (humans, whales, tigers) take longer to adapt

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Misconception about Natural Selection

• Fitness does not mean strongest> Fitness = reproductive success. Ability to

produce viable offspring.• Organisms cannot develop traits because they need

them or want them.> Genetic variation + natural selection makes

adaptive traits more common in a population.

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Other clarifications about evolution by natural selection• Evolution = changes in a population's genetic makeup

over time> Over time = over generations

• Natural selection is one of the mechanisms for evolution to occur. The other mechanisms include:> Mutation> Migration> Genetic drift (population bottleneck and founder

effect) > Horizontal gene transfer> Hybridization

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Coevolution

• Textbook: "a biological arms race" between interacting populations of different species.

• More broad description: Coevolution is when two or more species reciprocally affect each other's evolution.> Occurs when species interact closely with one

another– predator/prey– parasite/host– competitive species– mutualistic species

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Exampes of coevolution

http://evolution.berkeley.edu/evosite/evo101/IIIFCoevolution.shtml

Ants and Acacia--hollow thorns, secrete nectar at base for ants. Ants protect acacia against herbivores.

This yucca moth is inside the flower of a yucca, Yucca glauca. Photo by Ann Cooper, BugGuide.net.http://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/yucca_moths.shtml

Yucca and Yucca moth--The moth lays its eggs in the flower, and the larvae feed on the fruit. The moth pollinates flowers.

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Changes in the environment necessitates adaptation by natural selection.

• Geologic processes• Climate change• Catastrophes

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Geologic Processes

• Tectonic plates• Alfred Wegener• The Earth's lithosphere is broken up into a series of

giant solid plates.• These plates sit on the asthenosphere (a layer of

molten rock) and drift across the Earth's surface.

http://www.rsc.org/Education/Teachers/Resources/jesei/platerid/plates.htm

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Geologic Processes

• Effect on evolution:1. Locations of continents and oceans influences earth's

climate -->distribution of animals and plants2. Separation and joining of continents have allowed

species to move, adapt to new environments, and form new species by natural selection.

3. Volcanic eruptions (at plate boundaries) destroys habitats and reduce or wipe out populations. Opens up habitat to be repopulated. Lava can yield fertile soil (rich in nutrients like phosphorous and other minerals)

4. Earthquakes can separate and isolate populations (leads to speciation)

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Climate Change

• Repeated changes in earth's climate throughout history.

• Alternating periods of cooling and heating> Ice age and interglacial periods> During interglacial periods-ice melts, sea level

rises, ice sheets retreat

http://geology.utah.gov/surveynotes/gladasked/gladice_ages.htm

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Climate ChangeEffects on evolution:1. Determines where plants/animals can live

(distribution)2. Changes distribution of ecosystems--deserts,

grasslands, forests, etc.3. Some species become extinct when climate change

occurs rapidly.

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Catastrophes

• Asteroids and meteorites collide with earth. • Impact causes destruction of ecosystems and

extinction of species

Effects on evolution:• 1) Long period of environmental stress--wipe out

species and habitat• 2) Mass extinctions open up opportunities for new

species

Vredefort Crater, South Africa

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Ecological Niche

• Every species has a ecological niche, or a specific role in the ecosystem.> Where it lives/grows (habitat)> Where it reproduces and how> What it eats, how it eats.> How it interacts with other species and

environment.> "How an organism makes a living"

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Ecological Niche

• Fundamental niche - the full potential range of physical, chemical, and biological conditions and resources a species could theoretically use if it could avoid competition from other species.

• Realized niche - the actual niche a species occupies. Is only a part of the fundamental niche.

http://www.hammiverse.com/lectures/53/1.htmlFigure 53.13, page 1117, Campbell's Biology, 5th Edition

Experiment by Joseph Connell

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Ecological NicheGeneralist species have broad niches.• Can live in different places, eat many types of foods,

tolerate wide range of environmental conditions.• Better able to survive changing environment.

Specialist species occupy narrow niches.• Use only one/few types of food, tolerate narrow range

of environmental conditions.• More prone to extinction due to change in environment • Low competition when conditions constant

• Ex: Panda-only eats bamboo. Combined with habitat loss and low birth rate -> endangered

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Specialist Species

• Specialist species can allow for resource partitioning. Resource partitioning reduces competition and allows sharing of limited resources.

• When different species compete for scarce resources, natural selection results in more specialized species to reduce competition

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Speciation

• Speciation: formation of new species, two species arise from one.> For sexually reproducing species-when some

members of a population can no longer breed with other members to produce fertile offspring.

http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_42

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Mechanism of Speciation

• Reproductive isolation is the key to speciation: barriers to gene flow allow genetic differences to accumulate and result in different species.

• Reproductive isolation may occur due to> Different mating location, time, or rituals.> Lack of "fit" between sexual organs.> Offsprings not viable or fertile.

These damselfly penises illustrate just how complex insect genitalia may behttp://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_44

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Mechanism of Speciation

• Why does reproductive isolation occur? Reduced gene flow!

1) Allopatric speciation: Geographic Isolation-members of the same population become physically isolated. Adapt to different environmental conditions

> physical barriers (mountain range, stream, lake, road)

> volcanic eruptions> earthquake> individuals taken away by wind or water

http://evolution.berkeley.edu/evosite/evo101/VC1bAllopatric.shtml

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Mechanism of Speciation2) Peripatric speciation

A small number of individuals move into a new niche, and by chance (think genetic drift), have genes that are rare in the original population.

http://evolution.berkeley.edu/evosite/evo101/VC1cPeripatric.shtml

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Mechanism of Speciation3) Parapatric speciation• No extrinsic barrier to random mating, but population

mates non-randomly over a large geographic area. • More likely to mate with others in same geographic

location within population.

Although continuously distributed, different flowering times have begun to reduce gene flow between metal-tolerant plants and metal-intolerant plants.

http://evolution.berkeley.edu/evosite/evo101/VC1dParapatric.shtml

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Mechanism of Speciation4) Sympatric speciation• Does not require large-scale geographic distance

(physical isolation).• Disruptive selection.

http://evolution.berkeley.edu/evosite/evo101/VC1eSympatric.shtml

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Mechanism of Speciation

• These mechanisms of speciation occur very slowly--over many years.

• There are other mechanisms of evolution that can happen quickly (in one generation)> 1) Hybridization: Two individuals of different

species are able to mate and produce viable offspring. (often happens in plants by polyploidy).

> 2) Horizontal gene transfer

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Sexual Reproduction is adaptive--maintains genetic diversity in a population• Genetic diversity is important to be able to adapt to

constantly changing and challenging environment.• Remember traits are passed from parent to offspring

(vertical gene transfer)

Some microorganisms can exchange genes without sexual reproduction by horizontal gene transfer• Adaptations can occur

quickly--doesn't require generations.

• Confounds phylogenetic trees

http://www.nature.com/nrmicro/journal/v4/n1/fig_tab/nrmicro1325_F2.html

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Extinction

• Extinction: entire species ceases to exist.• Species become extinct when populations cannot

adapt to changing environmental conditions.• Endemic species = species that are only found in one

area. (Islands, small unique areas, highly specialized) are especially vulnerable to extinction.

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All species eventually become extinct.

• background extinction: ongoing extinction of species dues to changes in environmental conditions.> Estimated to be about 1-5 species for each

million species on earth.• mass extinction: widespread event of high

extinction rate. Large groups of existing species (25-70%) are wiped out.> Estimated there have been 5 mass extinctions

during past 500 million years.• mass depletion: extinction rates higher than normal

but not high enough to be considered mass extinction.

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When a mass extinction or mass depletion occurs, gives other species opportunity to fill previously occupied niches or newly created ones.

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Biodiversity = speciation - extinction

• Why is biodiversity important for the ecosystem?

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Human Effects on Earth's Biodiversity

• Human activities are decreasing earth's biodiversity.> As human population increases, resource

consumption increases.> Humans take over more of earth's surface and net

primary productivity.> Degrade or destroy habitats.

Do you remember the 5 ways in which people are accelerating species loss?

• H: habitat destruction and degradation• I: invasive species• P: Pollution• P: human population growth• O: Over exploitation

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Predictions by Stuart Primm and Edward O. Wilson (2005 Millenium Ecosystem Assessment)• Extinction rates have increased 100-1,000 times natural

background extinction rates.• By 2030: premature extinction of 1/5 earth's species.• Can we recover from these major losses?

> Species formed over millions of years.> Humans are depleting and destroying habitats with

in years.> Need to protect! (strategies to be discussed in later

units)

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Artificial Selection and Genetic Engineering

• Artificial selection: Selective breeding, humans breed certain animals or plants for certain desirable traits. > Relatively slow process: need to select

individuals, crossbreed, and repeat with offspring.> Also limited to species that are related.

http://en.wikipedia.org/wiki/File:Cornselection.jpg

http://en.wikipedia.org/wiki/Selective_breeding

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Artificial Selection and Genetic Engineering

• Genetic engineering: alteration of an organism's genetic material through adding, deleting, or changing segments of its DNA to produce desirable traits or eliminate negative ones.> Recombinant DNA: DNA that has been altered

or contain genes or portions of genes from organisms of different species.

> GMOs or transgenic organisms: organisms that have been genetically engineered using recombinant DNA

> Much faster than artificial selection, don't need to breed so can transfer genes from unrelated organisms.

September 30, 2014

Artificial Selection and Genetic Engineering

• Genetic engineering: alteration of an organism's genetic material through adding, deleting, or changing segments of its DNA to produce desirable traits or eliminate negative ones.> Biopharming: using genetically engineered

animals to act as biofactories for drugs, vaccines, antibodies, hormones, chemicals, organs

• Synthetic biology: use fundamental components of cells to rebuild new organisms> Cloning

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How to make a transgenic organism

• Identify gene of interest• Cut out and paste into a construct• Insert gene into organism of interest• Grow organism

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How to make a transgenic organism

• Identify gene of interest• Cut out and paste into a construct• Insert gene into organism of interest• Grow organism

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How to make a transgenic organism

• Identify gene of interest• Cut out and paste into a construct• Insert gene into organism of interest• Grow organism

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Get into groups of 3-4 and share your GMO's.

• Categorize your GMO's: you will present your categories and what GMOs are in your categories.

• Make a list of the benefits and/or concerns about GMOs.

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Concerns About the Genetic Revolution

• Not a controlled, predictable process: trial and error• Ethical issues (designer babies, selection of embryos,

genetic diseases/disorders)• Socioeconomic distribution of technology and its

benefits.• Consumer choice/information: Labeling of GMO's in food

labels• Disrupt ecosystems (pesticides kill natural predator

insects)• Accelerate genetic evolution (pesticide use)• Exploitation of developing countries resources by

developed countries• Food safety issues• Contamination of normal crops

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